This invention generally relates to the field of passive electronic countermeasures and more specifically to apparatus for deploying expendable materials such as chaff from a tactical aircraft.
The use of chaff to defeat the radar function by denying it range and direction (azimuth and elevation) information is a well known and practiced technique in the art of radar jamming and/or countermeasures. Passive chaff elements in the form of discrete dipoles are dispensed by an aircraft to form a distinct cloud which creates a credible false target to the ground-based radar. The dipoles are generally low mass slivers of metalized milar, glass or other suitable dialectric material and these are compactly and densely packaged into canisters and loaded into ejection equipment aboard the aircraft. The ejection equipment fires the chaff out of the canisters into the aircraft windstream where velocity-induced turbulence or wind shear effects are available for cloud dispersion. The low mass chaff slivers, upon ejection, rapidly slow down and fall at an almost constant rate. For example, a widely used one-mil metalized glass chaff has a settling rate of about 50 feet per minute.
One of the problems with present chaff systems is that the low mass slivers are easily damaged by the high compressive force necessary to eject them from the canister and into the aircraft windstream. Being compressed, the chaff dipoles may not uniformly disperse in the windstream and therefor will not provide the desired radar countermeasures performance. In actual practice, approximately one third of a pound of various length chaff dipoles are placed into the aircraft boundary layer in approximately 6-to-8 milliseconds. Dipoles from the ejected clumps peel off layer-by-layer until all that remains is a saturated cloud of dipoles 11/2-2 meters in width and height and 10-12 meters in length. Initial formation of the cloud takes approximately 200 milliseconds. At aircraft velocities on the order of 800 feet per second, cloud formation takes place well aft of the aircraft with a maximum cross section of approximately four square meters when viewed on a radial run.
From the foregoing, it can be appreciated that full chaff dispersion and/or cloud formation is desirable as soon as possible after the chaff are ejected from a loaded canister.
This invention provides an improved chaff ejection apparatus for deploying a quantity of dipoles, which apparatus imparts a vector to the chaff cloud that is transverse to the aircraft line-of-flight. This is accomplished by ejecting the chaff from a spin stabilized payload disk mounted in an ejection cartridge. As the payload disk is ejected from the cartridge, both high linear and rotational velocities are imparted to the disk and it emits the chaff dipoles in a substantially continuous manner as it moves out from the aircraft. When the spinning payload disk is ejected at an angle with respect to the aircraft line-of-flight (for example @ 90 degrees) and releasing chaff as it moves outwardly, a significant increase in cloud size is achieved while still in the vicinity of the launching aircraft. A particular advantage of the invention resides in the fact that the chaff dipoles are not compressively ejected from the aircraft, but rather, are packaged within an expendable disk. In this respect, the payload disk receives the force necessary for ejection leaving the chaff dipoles in their as-packaged condition. The self-protect ability of an aircraft is therefore enhanced by the rapid chaff cloud formation and its greater size when viewed by a ground-based radar.